It is known, for example from European Patent No EP0987431 in the name of Delphi Technologies Inc., to provide a fuel injector with two independently operable valve arrangements for controlling fluid pressure within the injector. The valve arrangements are arranged to control movement of a fuel injector valve needle relative to a valve needle seating so as to control the delivery of fuel from the injector. Movement of the valve needle away from the seating permits fuel to flow from the injector delivery chamber through one or more outlet openings of the injector into the engine or other combustion space.
A first one of the valve arrangements, known as a control valve arrangement or nozzle control valve, includes a control valve member which is movable between a first position in which fuel under high pressure is able to flow from a fuel supply passage into a control chamber, and a second position in which the control chamber communicates with a low pressure fuel reservoir. A surface associated with the valve needle is exposed to fuel pressure within the control chamber such that the pressure of fuel within the control chamber applies a force to the valve needle to urge the valve needle towards its seating, thereby closing the outlet openings. In this position, injection of fuel into the engine or other combustion space does not occur.
In order to commence injection, the control valve arrangement is actuated such that the control valve member is moved into its second position, thereby causing fuel pressure within the control chamber to be reduced. The force urging the needle towards its seating is therefore reduced and fuel pressure within the delivery chamber acts on thrust surfaces of the valve needle to lift the valve needle away from its seating to permit fuel to flow through the injector outlet openings.
In order to terminate injection, the control valve arrangement may be actuated such that the control valve member is moved into its first position, thereby permitting fuel under high pressure to flow from the fuel supply passage into the control chamber. The force acting on the valve needle due to fuel pressure within the control chamber is therefore increased, causing the valve needle to be urged against its seating to terminate injection.
It can be seen that the control valve arrangement is therefore operable effectively to control the pressure differential between the fuel in the control chamber and the fuel in the delivery chamber, that is to say the differential in the pressure acting to close the needle and the pressure serving to open it. In addition to the pressure of fuel in the control chamber tending to urge the valve needle to close, a closing spring is usually provided to assist the aforementioned closing force.
Another method of terminating injection is to use the second valve arrangement, often known as a “spill valve” or “drain valve”. The drain valve includes a drain valve member which is movable within a bore formed in a drain valve housing between a first, closed position in which pressurised fuel is able to flow from a high pressure fuel source, such as a fuel pump, to the fuel supply passage and the delivery chamber and a second, open position in which the fuel supply passage communicates with the low pressure fuel reservoir.
Movement of the drain valve to its open position causes fuel to flow from the fuel supply passage and the delivery chamber to the low pressure reservoir such that fuel pressure within the fuel supply passage and the delivery chamber is reduced. The resulting pressure differential between the control chamber and the delivery chamber urges the valve needle against its seating, closing the outlet openings in the injector body and terminating injection.
Movement of the drain valve member between the first and second positions is frequently achieved by means of an electromagnetic actuator and spring arrangement. Energisation of the actuator causes the drain valve member to move into the first, closed position whilst de-energising of the actuator causes the drain valve member to move into the second, open position under the influence of the spring.
Since the actuator is de-energised in order to move the drain valve member into the second position, there is little or no control of the movement of the drain valve member, which movement is determined mainly by the rate of the spring. As a result, the drain valve member is opened at a relatively high speed.
This high speed opening of the drain valve member has been shown to have an adverse effect on the structural integrity of the drain valve. Specifically, the abrupt contact between the drain valve member and the end wall or “stop face” of the drain valve housing exerts high stresses on the drain valve member which can fracture or distort. In addition, injector noise may be relatively high.
It is an aim of the invention to provide an improved valve arrangement which addresses some or all of the problems mentioned above or an injector having such an improved valve arrangement.